This invention relates to composite elastic materials useful for prosthetic applications, and prosthetic devices made therefrom.
Various silicone elastomer materials have been proposed for use in prosthetic devices such as suction liners of the type described in U.S. Pat. No. 4,923,474 granted to Klasson and Kristinsson on May 8, 1990. Other examples of such suction liners include U.S. Pat. No. 5,728,168 granted Mar. 17, 1998 to Laghi et al. and U.S. Pat. No. 5,830,237 granted to Kania Nov. 3,1998.
Composite elastomer materials useful for both suction liners and sealing sleeves are disclosed in U.S. Pat. No. 5,571,208 granted Nov. 5,1996 to Caspers.
It is highly desirable to provide a relatively soft cushion in contact with or adjacent the skin of the user of a prosthetic device for comfort. However, the cushion must be relatively inert with respect to the skin of the user, be readily washable and feel comfortable. Silicone elastomers and silicone gels are generally known for such applications and function satisfactorily as suction liners in sleeves both when the silicone material is used alone and when it is used in combination with an outer stretchable fabric covering.
It has been observed, however, that as the thickness of the silicone elastomer cushion grows, so does the weight of the suction liner. It is highly desirable to obtain the soft cushioning effect of a silicone elastomer in a suction liner application while reducing the overall weight of the liner attributable to the silicone elastomer.
In suction sleeves formed with a silicone elastomer liner, it is desirable to form a relatively thin posterior wall and a relatively thick anterior wall to provide cushioning on the anterior wall while avoiding interference with movement of the prosthetic user, particularly with a below-the-knee amputee. Such a configuration, on the other hand, generally requires a discontinuity of curvature in the transition regions between the anterior and posterior walls. This rapid transition in wall thickness and curvature can be a source of discomfort to a prosthetic user and it is desirable to avoid such rapid change in elastomer wall thickness in these transition regions.
The present invention is a composite elastic material particularly useful for prosthetic applications and that is formed of at least one cured silicone elastomer layer containing silicone oil and hollow microspheres dispersed throughout the elastomer layer.
The composite elastic material preferably also includes an elasticized fabric layer intimately bonded to one side of the silicone elastomer layer described above.
The composite elastic material may be used in the form of a tubular prosthetic suction liner having a closed distal end and dimensioned and configured so as to be rollable onto a distal end of a residual limb of a prosthetic device user, with a silicone elastomer layer on the interior of the liner and the elasticized fabric on the exterior of the liner. Such residual limb receiving liners are used between a socket of a prosthetic appliance and the residual limb of the appliance user.
The composite elastic material also may be used as a sealing sleeve that is tubular in form and open at opposed ends, with the silicone elastomer layer covering the inside wall of the sleeve and the elasticized fabric covering the exterior of the sleeve. Such a sleeve is dimensioned and configured to be installed as a suction seal between a prosthetic device and the residual limb of the prosthetic device user, with the silicone elastomer layer facing towards the location of the residual limb with the upper end of the prosthetic device located within the sleeve.
When used in a suction liner, the composite elastic material may include a distension controlling reinforcement matrix embedded in the silicone elastomer layer over a distal end area of the suction liner, wherein the reinforcement matrix, for example a circular knit textile, contains reinforcement elements that provide substantial stiffness against elongation of the liner in a direction along the liner length but which do not provide substantial resistance against distension of the silicone elastomer layer in directions transverse to the liner length.
A rigid prosthetic connector element may be attached to the distal end of the suction liner by embedding the connector element in a cured silicone elastomer distal end cap adhered to the distal end of the suction liner. The connector is sufficiently exposed while embedded in the end cap so as to provide access to a prosthetic connector pin that may be fastened to the connector. The silicone elastomer distal end cap may be formed of a silicone elastomer having a higher durometer than the composite elastic silicone elastomer layer to provide a more rigid support zone at the distal end of the suction liner.
The microspheres used in the composite elastic material preferably are expanded polymeric shells having a density of 0.005 g/cm3 to 1.25 g/cm3, preferably 0.05 g/cm3.
The silicone elastomer layer preferably comprises, by weight, 50-99.4% silicone elastomer; 0.5-45% silicone oil; and 0.1-5% microspheres. Preferably, the ratio of silicone elastomer, silicone oil and microspheres is: 77.25% silicone elastomer; 10% silicone oil and 0.75% microspheres (by weight).
Preferably, the silicone elastomer material of the composite elastic material is blended with one or more skin treating agents such as Vaseline (Petroleum jelly) and aloe Vera. For example, the silicone elastomer may be blended with up to 3% aloe vera by weight of the silicone elastomer layer, with the balance of the skin treatment agent constituting Vaseline, so that the silicone elastomer layer is blended with skin treatment agents up to about 20% by weight of the silicone elastomer layer.
The composite elastic material containing silicone elastomer, silicone oil, and microspheres preferably has a density of 0.5 g/cm3 to 1.3 g/cm3; a tensile strength of at least 0.1 Pa; a durometer (00) of 13-62; a 100% modulus of 5 kPa to 250 kPa; and a compression set of 0 to 30.
The invention also contemplates a suction liner formed of the composite elastic material in accordance with the invention wherein the suction liner is tapered conically inwardly towards its distal end from its open proximal end, and wherein the sleeve has a circular outer wall having radii of curvature centered along a first longitudinal sleeve axis of external symmetry extending longitudinally centrally within the sleeve, a circular curved inside anterior wall portion extending along a sleeve length and having first radii of curvature centered on a second longitudinal axis of anterior curvature extending longitudinally along said sleeve length and a circular curved inside posterior wall portion having second radii of curvature centered on a third longitudinal axis of posterior curvature extending along said sleeve length; said first, second and third longitudinal axes lying in a common longitudinally and transversely extending plane bisecting the anterior and posterior wall portions, and wherein said second and third axes are spaced apart at predetermined offset distance on opposed sides of said first axis to thereby define an anterior wall portion that is thicker along the sleeve length than the posterior portion; and further wherein the anterior and posterior wall portions intersect each other along said sleeve length on the sleeve interior along diametrically opposed inner transition wall portions that extend tangentially relative to the adjoining anterior and posterior wall portions along said sleeve length, whereby the interior wall of the suction sleeve along the transition wall portions is free of rapid changes in thickness, curvature or cross-section profile.
Preferably, the second and third radii of curvature are equal to each other along their respective second and third axes.
A spherical curved inside distal wall portion may be provided within the suction liner, said distal wall portion joining the adjoining interior wall of the suction liner along a tangency that forms a smooth transition between the inside distal wall portion and the adjoining interior wall of the suction liner. The thickness of the adjacent interior wall of the suction liner may be the same as the thickness of the anterior wall of the suction liner.
When provided with an elasticized fabric layer bonded on one side of the silicone elastomer layer, a thin continuous coating of second cured elastomer material is provided on the elasticized fabric between the fabric and the principal silicone elastomer layer. The thin coating of the second elastomer material partially penetrates and is embedded in the fabric layer and forms a continuous coating over the textile material between the textile and the principal silicone elastomer layer. The silicone elastomer coating material is fully stretchable elastically at least to same extent as the elasticized fabric layer to which it is attached and adhered.
When the composite elastic material is formed into a sealing sleeve with an elasticized textile fabric layer bonded on one side of the silicone elastomer layer, the textile fabric may be a circular rib knit formed principally of Nylon with a small amount of Lycra (a fiber available from DuPont) or other stretchable fiber. A secondary coating of cured silicone elastomer material may be used between the principal silicone elastomer layer and the fabric, in the same manner as described above.